Calibrating a serial interconnection

ABSTRACT

A method for calibrating a serial interconnection system having a first node, a second node, calibration nodes that are electrically connected in series by the serial interconnection system, and connection nodes corresponding to the serially connected calibration nodes, the connection nodes electrically connected in series by the serial interconnection system, the calibration method involving: for each of the calibration nodes performing a measurement procedure involving: injecting a corresponding reference signal into that calibration node; and while the corresponding reference signal is being injected into that calibration node, measuring the phase difference of signals appearing at the first and second nodes; from the measured phase differences for the calibration nodes, computing phase corrections for each of the calibration nodes; and applying the phase corrections computed for each of the calibration nodes to the corresponding connection nodes.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.62/216,592, filed Sep. 10, 2015, all of which is incorporated herein byreference.

TECHNICAL FIELD

Embodiments of the present invention generally relate to signaldistribution networks, which may be used in applications such as LocalOscillator (LO) distribution for analog phased arrays, sampling clockdistribution for digital phased arrays, or clock distribution fordigital integrated circuits.

BACKGROUND

A serial interconnection between separate system modules provides thesimplest communication network between these modules. Due to itssimplicity, this type of network is useful in practice for cost andreliability reasons. In general, a system module can be any subsystem,as simple as a single passive component or as complicated as aPhased-Locked Loop (PLL), an entire radio, an antenna phased array, orsome other complex circuit. A serial interconnection uses a transmissionmedium with unidimensional signal propagation properties such as anelectrical cable, an optical fiber, a strip line, a microstrip line, acoplanar line, a wireless narrow beam, etc. The system modules connectedserially attach to this transmission medium and receive or transmitsignals, usually according to a protocol. For example, a simple protocolinvolves distributing a signal from one module to all other modules. Amore sophisticated protocol might involve both transmitting andreceiving signals from one module to any other module or set of modules.

In many applications, it is important to know precisely the time delay asignal undergoes when propagating over the serial interconnection fromone module to another module. For example, if we distribute serially anLO (local oscillator) or a sampling signal over a phased arraycontaining many radio modules, it is important to correct the phasedifferences between the signals received at each radio module due topropagating delays. Without this correction, also referred to as “phasecalibration”, the proper functionality of the phased array would becompromised since the very operation of a phased array relies on preciseglobal phase alignment of signals at all radios.

Similarly, in some applications not only time delays or phase shifts butalso signal magnitude changes due to transmission loses or other effectsmust be corrected. For example, the Intermediate Frequency (IF) lines inthe active arrays described in U.S. Pat. No. 8,611,959, filed Dec. 17,2013, all of which is incorporated herein by reference, have practicallosses in addition to phase shifts. These losses need to be compensatedfor correct system operation. The magnitude correction is also called“magnitude calibration”.

In production samples, time delays producing phase shifts and magnitudechanges due to signal transport over a serial interconnection can becalculated or directly measured. However, such methods can be used forphase/magnitude calibration only if the physical implementation of theserial interconnection has transmission properties which are predictableto the desired precision after manufacturing and do not varyunpredictably over expected changes in operating conditions, such astemperature and humidity. If, for example, the transmission propertiesof the serial interconnection are subject to manufacturing variationsbeyond the desired precision, any pre-production calculations andsimulations or any direct measurements of production samples cannotrepresent correctly the transmission properties of all units produced.

Likewise, even if all production units have predictable transmissionproperties at factory temperature and humidity conditions, theseproperties might vary unpredictably beyond the desired precision withfield operating conditions. In such cases, the methods described abovefor identifying time delays and magnitude changes of serialinterconnects cannot be used to compensate correctly the time delays andmagnitude changes in the field.

When phase/magnitude calibration of a serial interconnection isrequired, the usual practice is to fabricate the serial interconnectionwith materials and design techniques ensuring predictablecharacteristics over manufacturing and operating conditions. This comeswith a significant cost penalty in most cases. Take, for example, aphased array, which is a large electrical system, i.e., a system withphysical dimensions large compared to the wavelength of the operatingfrequency. If high frequency signals such as LO (local oscillator)signals propagate through the phased array over a serialinterconnection, very large phase skews occur (e.g., thousands ofdegrees) yet the compensation of these skews (phase calibration) mustreduce them to only a few degrees. This cannot be accomplished unlessthe natural skews are predictable to this level of precision. In orderto fabricate transmission lines with such accurate characteristics,expensive materials (e.g. dielectrics, etc.) and high fabricationtolerances (e.g. line widths, thicknesses, etc.) are required.

A low cost method for designing serial interconnections with inherentphase calibration is described in U.S. Pat. No. 8,259,884, filed Jul.21, 2008, all of which is incorporated herein by reference. Otherapproaches to the same effect are also described in prior art identifiedin U.S. Pat. No. 8,259,884. In these methods, rather than relying onexpensive materials and fabrication tolerances, the design relies onmutual compensation between signals propagating over matchedtransmission lines. These methods further rely on various high precisionanalog circuits. In practice, these analog circuits are challenging todesign and are difficult to scale or port from one implementation toanother because they require operation at high speed and with highprecision simultaneously.

SUMMARY

Here we disclose new methods for phase/magnitude calibration of serialinterconnections without relying on predictable transmissioncharacteristics of the serial interconnections. Unlike prior artmethods, these new methods are also naturally fit for implementationwith low-cost, scalable and portable digital circuits in lieu of analogcircuits. Furthermore, some of the new methods do not rely on matchedtransmission lines.

For clarity and simplicity, the new concepts are introduced anddescribed using continuous wave (CW) signals, i.e., signals containing asingle frequency or tone. However, these concepts are valid for morecomplex signals such as modulated bandpass signals used in communicationsystems. For example, a phase calibration at one particular frequency isusually valid over a range of frequencies close to the calibratingfrequency.

The methods presented here for calibrating serial interconnections canalso be regarded as methods for distributing in serial manner coherent,phase-synchronized and equal magnitude signals to multiple points. Thiswill be obvious through the descriptions following below.

In general, in one aspect, at least one of the inventions features amethod for calibrating a serial interconnection system having a firstnode, a second node, a plurality of calibration nodes that areelectrically connected in series by the serial interconnection system,and a plurality of connection nodes corresponding to the plurality ofserially connected calibration nodes, the plurality of connection nodeselectrically connected in series by the serial interconnection system,the calibration method involving: for each of the plurality ofcalibration nodes performing a measurement procedure involving:injecting a corresponding reference signal into that calibration node;and while the corresponding reference signal is being injected into thatcalibration node, measuring the phase difference of signals appearing atthe first and second nodes; from the measured phase differences for theplurality of calibration nodes, computing phase corrections for each ofthe plurality of calibration nodes; and applying the phase correctionscomputed for each of the plurality of calibration nodes to thecorresponding plurality of connection nodes.

Other embodiments include one or more of the following features. Themethod further involves: injecting a first reference signal into thefirst node; while the first reference signal is being injected into thefirst node, measuring the phase difference of that injected firstreference signal into the first node and a signal appearing at thesecond node; wherein computing phase corrections for each of theplurality of calibration nodes also employs the measured phasedifference for the first node as well as the measured phase differencesfor the plurality of calibration nodes. For each of the plurality ofcalibration nodes, the measurement procedure also involves while thecorresponding reference signal is being injected into that calibrationnode, measuring the magnitude ratio of the signals appearing at thefirst and second nodes, and the method further involves: from themeasured magnitude ratios for the plurality of calibration nodes,computing magnitude corrections for each of the plurality of calibrationnodes; and applying the magnitude corrections computed for each of theplurality of calibration nodes to the corresponding plurality ofconnection nodes. The method further involves: injecting a firstreference signal into the first node; while the first reference signalis being injected into the first node, measuring the phase differenceand the magnitude ratio of that injected first reference signal and asignal appearing at the second node; wherein computing phase andmagnitude corrections for each of the plurality of calibration nodesalso employs the measured phase difference and magnitude ratio for thefirst node.

Still other embodiments include one or more of the following features.The serial interconnection system includes a first serialinterconnection serially interconnecting the first node, the pluralityof connection nodes, and the second node, wherein the plurality ofcalibration nodes is the same as the plurality of calibration nodes.Alternatively, the serial interconnection system includes a first serialinterconnection serially interconnecting the first node, the pluralityof calibration nodes, and the second node and a second serialinterconnection serially interconnecting the plurality of connectionnodes, wherein the first serial interconnection and the second serialinterconnection are separate.

The portion of the first serial interconnection that seriallyinterconnects the plurality of calibration nodes and the portion of thesecond serial interconnection that serially interconnects the pluralityof connection nodes are electrically matched. Alternatively, the serialinterconnection system includes a first serial interconnection seriallyinterconnecting the second node and the plurality of calibration nodes,a second serial interconnection serially interconnecting the first nodeand the plurality of calibration nodes, and a third serialinterconnection serially interconnecting the plurality of connectionnodes. The portion of the first serial interconnection that seriallyinterconnects the plurality of calibration nodes, the portion of thesecond serial interconnection that serially interconnects the pluralityof connection nodes, and the portion of the third serial interconnectionthat serially interconnects the plurality of connection nodes areelectrically matched.

Yet other embodiments of the invention include one or more of thefollowing features. While performing the measurement procedure for anyone of the plurality of calibration nodes, applying no other referencesignals to any of the other calibration nodes among the plurality ofcalibration nodes. The plurality of connection nodes is the same as theplurality of calibration nodes. The corresponding reference signals forthe plurality of calibration nodes have the same frequency.

In general, in yet another aspect, at least one of the inventionsfeatures a method for calibrating a serial interconnection system havingan input node, a first node, a second node, a plurality of calibrationnodes that are electrically connected in series by the serialinterconnection system, and a plurality of connection nodescorresponding to the plurality of serially connected calibration nodes,said plurality of connection nodes also electrically connected in seriesby the serial interconnection system. The calibration method involving:for each of the plurality of calibration nodes performing a measurementprocedure involving: injecting a corresponding reference signal intothat calibration node; and while the corresponding reference signal isbeing injected into that calibration node, measuring the phasedifference of signals appearing at the first and second nodes; from themeasured phase differences for the plurality of calibration nodes,computing phase corrections for each of the plurality of calibrationnodes; and applying the phase corrections computed for each of theplurality of calibration nodes to the corresponding plurality ofconnection nodes.

Other embodiments include one or more of the following features. Theserial interconnection system also includes an input node and the methodfurther involves: injecting a first reference signal into the input nodeand the first node; while the first reference signal is being injectedinto the input node and the first node, measuring the phase differenceof that injected first reference signal at the input node and a signalappearing at the second node, wherein computing phase corrections foreach of the plurality of calibration nodes also employs the measuredphase difference for the input node as well as the measured phasedifferences for the plurality of calibration nodes. For each of theplurality of calibration nodes the measurement procedure also involveswhile the corresponding reference signal is being injected into thatcalibration node, measuring the magnitude ratio of the signals appearingat the first and second nodes, and the method further involves: from themeasured magnitude ratios for the plurality of calibration nodes,computing magnitude corrections for each of the plurality of calibrationnodes; and applying the magnitude corrections computed for each of theplurality of calibration nodes to the corresponding plurality ofconnection nodes. The method further involves: injecting a firstreference signal into the input node and the first node; while the firstreference signal is being injected into the input node and the firstnode, measuring the phase difference and magnitude ratio of thatinjected first reference signal at the input node and a signal appearingat the second node, wherein computing phase and magnitude correctionsfor each of the plurality of calibration nodes also employs the measuredphase difference and magnitude ratio for the input node.

Yet other embodiments include one or more of the following features. Theserial interconnection system includes a first serial interconnectionserially interconnecting the first node and the plurality of calibrationnodes, and a second serial interconnection serially interconnecting theinput node and the plurality of connection nodes. The portion of thefirst serial interconnection that serially interconnects the pluralityof calibration nodes and the portion of the second serialinterconnection that serially interconnects the plurality of connectionnodes are electrically matched.

In general, in yet another aspect, at least one of the inventionsfeatures an apparatus including: a serial interconnection system havinga first node, a second node, a plurality of calibration nodes that areelectrically connected in series by the serial interconnection system,and a plurality of connection nodes corresponding to the plurality ofserially connected calibration nodes, the plurality of connection nodeselectrically connected in series by the serial interconnection system; aphase detector electrically connected to the first and second nodes ofthe serial interconnection system for measuring a phase difference ofsignals sensed at the first and second nodes; a plurality of switchablycontrolled signal sources, each switchably controlled signal sourceconnected to a different corresponding one of the plurality ofcalibration nodes; and a controller system. The control system isprogrammed to perform the functions of: for each of the plurality ofcalibration nodes, performing a measurement procedure involving: causingthe switchably controlled signal source for that calibration node toinject a corresponding reference signal into that calibration node; andwhile the corresponding reference signal is being injected into thatcalibration node, causing the phase detector to measure the phasedifference of signals appearing at the first and second nodes; from themeasured phase differences for the plurality of calibration nodes,computing phase corrections for each of the plurality of calibrationnodes; and applying the phase corrections computed for each of theplurality of calibration nodes to the corresponding plurality ofconnection nodes.

Other embodiments include one or more of the following features. Theapparatus further includes a switchably controlled first signal sourceconnected to the first node, and wherein the controller system isfurther programmed to perform the functions of: causing the switchablycontrolled first signal source to inject a first reference signal intothe first node; while the first reference signal is being injected intothe first node, causing the phase detector to measure the phasedifference of that injected first reference signal and a signalappearing at the second node, wherein computing phase corrections foreach of the plurality of calibration nodes also employs the measuredphase difference for the input node. The apparatus further includes amagnitude detector electrically connected to the first and second nodesof the serial interconnection system for measuring a magnitude ratio ofsignals sensed at the first and second nodes, and wherein for each ofthe plurality of calibration nodes, the measurement procedure for thatnode further involves, while the corresponding reference signal is beinginjected into that calibration node, causing the magnitude ratiodetector to measure the magnitude ratio of signals appearing at thefirst and second nodes, and wherein the controller system is furtherprogrammed to perform the functions of: from the measured magnituderatios for the plurality of calibration nodes, computing magnitudecorrections for each of the plurality of calibration nodes; and applyingthe magnitude corrections computed for each of the plurality ofcalibration nodes to the corresponding plurality of connection nodes.

Still other embodiments include one or more of the following features.The apparatus further includes: a switchably controlled first signalsource connected to the first node; and wherein the controller system isfurther programmed to perform the functions of: causing the switchablycontrolled first signal source to inject a first reference signal intothe first node; while the first reference signal is being injected intothe first node, causing the phase and magnitude ratio detectors tomeasure the phase difference and magnitude ratio of that injected firstreference signal and a signal appearing at the second node, whereincomputing phase and magnitude corrections for each of the plurality ofcalibration nodes also employs the measured phase difference andmagnitude ration for the input node.

Still yet other embodiments include one or more of the followingfeatures. The serial interconnection system includes a first serialinterconnection serially interconnecting the first node, the pluralityof connection nodes, and the second node, and wherein the plurality ofcalibration nodes is the same as the plurality of calibration nodes.Alternatively, the serial interconnection system includes a first serialinterconnection serially interconnecting the first node, the pluralityof calibration nodes, and the second node and a second serialinterconnection serially interconnecting the plurality of connectionnodes, wherein the first serial interconnection and the second serialinterconnection are separate. The portion of the first serialinterconnection that serially interconnects the plurality of calibrationnodes and the portion of the second serial interconnection that seriallyinterconnects the plurality of connection nodes are electricallymatched. Alternatively, the serial interconnection system includes afirst serial interconnection serially interconnecting the second nodeand the plurality of calibration nodes, a second serial interconnectionserially interconnecting the second node and the plurality ofcalibration nodes, and a third serial interconnection seriallyinterconnecting the plurality of connection nodes. The portion of thefirst serial interconnection that serially interconnects the pluralityof calibration nodes, the portion of the second serial interconnectionthat serially interconnects the plurality of connection nodes, and theportion of the third serial interconnection that serially interconnectsthe plurality of connection nodes are electrically matched. Thecontroller system is further programmed to cause the switchablycontrolled signal sources for the plurality of calibration nodes toinject corresponding reference signals into the plurality of calibrationnodes only one at a time. The corresponding reference signals for theplurality of calibration nodes have the same frequency.

In general, in still yet another aspect, at least one of the inventionsfeatures an apparatus including: a serial interconnection system havingan input node, a first node, a second node, a plurality of calibrationnodes that are electrically connected in series by the serialinterconnection system, and a plurality of connection nodescorresponding to the plurality of serially connected calibration nodes,the plurality of connection nodes also electrically also connected inseries by the serial interconnection system; a phase detectorelectrically connected to the first and second nodes of the serialinterconnection system for measuring a phase difference of signalssensed at the first and second nodes; a plurality of switches forswitchably electrically connecting each connection node among theplurality of connection nodes to a corresponding different calibrationnode among the plurality of calibration nodes; a controller systemprogrammed to perform the functions of: for each of the plurality ofcalibration nodes, performing a measurement procedure involving: causingthe switch for that calibration node to inject a corresponding referencesignal from the corresponding connection node into that calibrationnode; and while the corresponding reference signal is being injectedinto that calibration node, causing the phase detector to measure thephase difference of signals appearing at the first and second nodes;from the measured phase differences for the plurality of calibrationnodes, computing phase corrections for each of the plurality ofcalibration nodes; and applying the phase corrections computed for eachof the plurality of calibration nodes to the corresponding plurality ofconnection nodes.

Other embodiments include one or more of the following features. Theapparatus further includes a magnitude detector electrically connectedto the first and second nodes of the serial interconnection system formeasuring a magnitude ratio of signals sensed at the first and secondnodes, and wherein for each of the plurality of calibration nodes, themeasurement procedure for that node further involves, while thecorresponding reference signal is being injected into that calibrationnode, causing the magnitude detector to measure the magnitude ratio ofsignals appearing at the first and second nodes; and wherein thecontroller system is further programmed to perform the functions of:from the measured magnitude ratios for the plurality of calibrationnodes, computing magnitude corrections for each of the plurality ofcalibration nodes; and applying the magnitude corrections computed foreach of the plurality of calibration nodes to the correspondingplurality of connection nodes. The serial interconnection system alsoincludes an input node, and the apparatus further includes a signalsource electrically connected to the input node. The apparatus furtherincludes a first switch for switchably electrically connecting the inputnode to the first node, and wherein the controller system is furtherprogrammed to perform the functions of: causing the first switch toinject a signal into the first node from the input node; while thesignal is being injected into the first node from the input node,causing the phase and magnitude detectors to measure the phasedifference and the magnitude ratio of that signal injected into thefirst node from the input node and a signal appearing at the secondnode, wherein computing phase and magnitude corrections for each of theplurality of calibration nodes also employs the measured phasedifference and magnitude ratio for the input node.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a simplified schematic diagram of a first method forphase and magnitude calibration of a serial distribution network.

FIG. 2 depicts a simplified schematic diagram of a possible PD/MRDetector and Controller (CTR).

FIG. 3 depicts a simplified schematic diagram of a second method forphase and magnitude calibration of a serial distribution network.

FIG. 4 depicts a simplified schematic diagram of a third method forphase and magnitude calibration of a serial distribution network.

FIG. 5 depicts a simplified schematic diagram of a fourth method forphase and magnitude calibration of a serial distribution network.

FIG. 6 is a flow chart of an algorithm for calibrating a serialinterconnection as described herein.

FIG. 7 is a diagram of an analog phased array in which the calibrationtechniques described herein can be used.

FIG. 8 depicts an approach for calibrating a serial interconnection forphased array calibration.

DETAILED DESCRIPTION

A First Method for Calibrating a Serial Interconnection

A first phase/magnitude calibration method will be described with thehelp of the system illustrated in FIG. 1 but it should be understoodthat the principle of this method is more general than the specificimplementation shown in FIG. 1. A serial interconnection 1 a links twoend points X and Y with intermediate points A and B. An input signalgenerator 2 providing input signals to the system is coupled to serialinterconnection 1 a at the end point X through a switch 3. If switch 3is on, input signal generator 2 can send signals through serialinterconnection 1 a to many points on this serial link including pointsX, A, B, and Y.

A signal applied at point X by input signal generator 2 arrives at pointA with a phase difference Φ₁ compared to the phase of the signal atpoint X and a magnitude, whose ratio to the magnitude of the signal atpoint X is α₁. As this signal travels further towards end point Y, itreaches point B with a phase difference ΔΦ compared to the phase atpoint A and with a magnitude whose ratio to the magnitude at point A isα. Finally, this signal reaches end point Y with a phase difference Φ₂compared to the phase of the signal at point A and a magnitude whoseratio to the magnitude of the signal at point A is α₂. A first objectiveof this calibration method is to determine the quantities Φ₁, Φ₂, ΔΦ,α₁, α₂, and α without assuming that the transmission properties ofserial interconnection 1 a are predictable over the entire or anyportion of serial interconnection 1 a. Furthermore, we assume that anysignal sources or circuits coupled to points X, A, B, and Y have noaccess to any global phase and magnitude references and therefore haveno means of determining how the phases and magnitudes of the signals attheir respective nodes relate to the phases and magnitudes at the othernodes. These conditions occur in many practical applications whereserial connectivity is used.

An additional assumption for the first phase/magnitude calibrationmethod is that the operating frequency in the system of FIG. 1 is knownat all nodes. This is not a fundamental or hard limitation because theoperating frequency can be communicated over the Serial Interconnection1 a from connection point X to all other connection points including A,B, and Y during the initialization of the system (before starting thephase/magnitude calibration process). One way of doing this is by addingtunable frequency references at points A, B, and Y (not shown in FIG.1), which would adjust to the frequency of input signal generator 2during system initialization. In this way, connection points A, B, and Yobtain and maintain knowledge of the operating frequency at connectionpoint X. It is emphasized that while transferring knowledge of theoperating frequency from point X to A, B and X is straightforward, asmentioned above, the phase and magnitude changes occurring over serialinterconnection 1 a remain unknown before the methods described in thisapplication are applied.

Using only two intermediate points (A and B) in the system of FIG. 1 issufficient to explain the first calibration method as well as othercalibration methods to be introduced later. However, this first andother calibration methods described herein remain valid even if we addas many intermediate points as necessary to suit any particularapplication. This will become more apparent after the methods aredescribed.

Serial interconnection 1 a may be a simple transmission line properlyterminated at both ends or any other passive or active serialconnectivity. One requirement for serial interconnection 1 a is topropagate signals in both directions without reflections at the endpoints or at any intermediate points. Another requirement is to split aninjected signal at an intermediate point into components launching inopposite directions with known relative phases and magnitudes (e.g. samephase and equal magnitudes, or with a known phase difference and a knownmagnitude ratio). In other words, any signal injected into serialinterconnection 1 a at an intermediate point is assumed to splitpredictably into components, which travel in opposite directions towardsthe end points, these components not generating reflections as they passby other intermediate points and getting fully absorbed at the endpoints by appropriate terminations. If a signal is injected at one ofthe end points, it will produce only a single component travellingtowards the other end point.

The system in FIG. 1 further contains a subsystem 4 coupled to the twoend points of serial interconnection 1 a and capable of detecting thephase difference and magnitude ratio between the signals at the endpoints. For this reason, subsystem 4 is called aphase-difference/magnitude-ratio detector or PD/MR detector 4. PD/MRdetector 4 passes to a controller (CTR) 10 the phase difference andmagnitude ratio values it detects from the end points of serialinterconnection 1 a. CTR 10 has control bus 11 for turning on and offswitch 3 and (switchably-controlled) signal sources 100, 101, and 102independently (e.g., using separate digital addresses). These signalsources 100, 101, and 102 are coupled to serial interconnection 1 a atconnection points X, A, and B, respectively, and are assumed to have thesame operating frequency as the signal of input signal generator 2 butarbitrary phases and magnitudes without any mutual relationships. Thecoupling of these sources to serial interconnection 1 a can be done bydirect connections, by capacitive couplers, by inductive couplers, or byany other non-directional signal coupling methods.

Also, through control bus 11, the CTR 10 can set the states ofcalibration circuits 5 independently. Each calibration circuit 5 iscoupled to serial interconnection 1 a at connection point A or B,respectively, and receives a signal from this node. Calibration circuit5 shifts the phase and scales the magnitude of the received signal andoutputs the resulting signal at nodes A1 or B1, respectively. The stateof calibration circuit 5 defines the amount of phase shift and magnitudescaling done by calibration circuit 5. A typical calibration circuit 5is a serial combination of a Variable Gain Amplifier (VGA) with aprogrammable phase shifting or phase rotator circuit.

In general, the PD/MR detector 4 and CTR 10 can be implemented invarious ways with the use of analog, digital, mixed-signal circuits, andpossibly with software. A preferred implementation is shown in FIG. 2where the PD/MR detector 4 has two analog-to-digital converters (ADC) 41and a digital processor (DP) 42, and where the CTR is a digitalcontroller (DCTR) 12. DP 42 and DCTR 12 are implemented in softwarerunning on a digital signal processor (DSP) 20.

The two analog-to-digital converters (ADC) 41 digitize the two inputsignals 13, which are received from the end points X and Y of serialinterconnection 1 a of FIG. 1. In cases where direct digitization of thesignals 13 is impractical (e.g. signal frequency too high for ADCsused), a downconverter (e.g. mixer) is added before digitization (notshown in FIG. 2 and assumed included in the ADC block 41). DP 42extracts the phase and magnitude values from the two digitized signals(e.g. by Fourier transform or similar techniques) and performs phasesubtraction and magnitude division for ratio calculation. DCTR 12performs the sequential control steps and calculations necessary fordetecting and compensating the phase and magnitude changes in serialinterconnect 1 a. These control steps and calculations are describednext, and are valid in principle for any other implementations of PD/MRdetector 4 and of CTR 10, not just for the example implementation shownin FIG. 2.

The detection of phase/magnitude changes in serial interconnection 1 ain FIG. 1 is done as follows. CTR 10 first turns off switch 3 in FIG. 1,blocking the input signal from being coupled into serial interconnection1 a. Then, CTR 10 turns on signal source 100 while signal sources 101and 102 are off. PD/MR detector 4 detects the overall phase differencePD0=Φ₁+Φ₂ and the overall magnitude ratio MR0=α₁*α₂ and passes thesevalues to CTR 10, which stores them. The equations above for PD0 and MR0follow simply from the fact that phases add and gains (magnitude ratios)multiply over a serial link. Also, notice that the values PD0 and MR0are independent of the absolute phase and magnitude values of the signalproduced by signal source 100.

Next, CTR 10 turns off signal source 100 and turns on signal source 101.This time PD/MR detector 4 detects a phase difference PD1=Φ₁−Φ₂ and amagnitude ratio MR1=α₁/α₂, assuming the signal of source 101 splitsequally into components travelling in opposite directions over serialinterconnection 1 a. These equations follow from the propagationconditions of the signal from source 101. Once again, PD/MR detector 4passes the values PD1 and MR1 to CTR 10, which stores them. Just asbefore, these values are independent of the absolute phase and magnitudevalues of the signal produced by signal source 101. Based on informationnow available, CTR 10 may calculate quantities Φ₁, Φ₂, α₁, and α₂ as asolution for a simple system of four equations with four unknowns (twoequations for the phase differences Φ₁ and Φ₂ and two equations for themagnitude ratios α₁ and α₂). This solution is Φ₁=(½)*(PD0+PD1),Φ₂=(½)*(PD0−PD1), α₁=SQRT(MR0*MR1), and α₂=SQRT(MR0/MR1), where SQRT(x)is the square root function.

The same process continues for point B. CTR 10 turns off signal source101 and turns on signal source 102. PD/MR detector 4 detects a phasedifference PD2=Φ₁−Φ₂+2*ΔΦ and a magnitude ratio MR2=α²*α₁/α₂, assumingthe signal of source 102 splits equally into components travelling inopposite directions over serial interconnection 1 a. The quantities PD2and MR2 are independent of the absolute phase and magnitude values ofthe signal produced by signal source 102. PD/MR detector 4 passes thesevalues to CTR 10, which stores them. Notice that the values PD2 and MR2can be expressed in terms of PD1 and MR1 as follows: PD2=PD1+2*ΔΦbecause PD1=Φ₁−Φ₂ and MR2=α²*MR1 because MR1=α₁/α₂. CTR 10 calculatesthe values ΔΦ and α by solving the two simple equations above. Theresults are: ΔΦ=(½)(PD2−PD1) and α=SQRT(MR2/MR1). These results areconsistent with the fact that the relative changes in phase andmagnitude from point A to B are independent of the phase and magnitudechanges from point X to A. In some applications such as phased antennaarrays (see FIG. 7), only the relative changes in phase and magnitudefrom one antenna element to another (e.g. from one point on serialinterconnection 1 a to another) are relevant. In these cases, signalsource 100 is not necessary and can be eliminated.

After CTR 10 has determined the values Φ₁, Φ₂, ΔΦ, α₁, α₂, and a (aswell as additional similar quantities if there are more points on serialinterconnection 1 a to be compensated) according to the method describedabove, CTR 10 sets the states of calibration circuits 5 in order toreverse the phase and magnitude changes occurring at points A and B dueto signal transport over serial interconnection 1 a. The desired resultis that when the signal of input signal generator 2 is switched intoserial interconnection 1 a through switch 3, it arrives at points A1 andB1 in phase and with equal magnitudes. CRT 10 sets the phase andmagnitude shifts of calibration circuits 5 with appropriate values,which can be calculated directly from the values of Φ₁, Φ₂, ΔΦ, α₁, α₂,and α. For example, the equalization of point A1 with respect to point Xis accomplished by setting a N*π-Φ₁ phase shift (where N is an integer)and a 1/α₁ magnitude scaling in calibration circuit 5 connected to pointA. In this way, the phases and magnitudes at points A1 and X becomeequal. The addition of the N*π phase shift is necessary in practice toinsure that we have a causal system (phase always advances with time).Similarly, the equalization of point B1 with respect to point A1 isaccomplished by setting a ΔΦ phase shift and an a magnitude scaling incalibration circuit 5 connected to point A and a zero phase shift andunity magnitude scaling in calibration circuit 5 connected to point B.Notice that this calibration choice is not unique as other states ofcalibration circuits 5 at points A and B will also result in validphase/magnitude calibrations.

An important property of this first method is that it requires nomatching of any parameters, signal sources, or other components, exceptfor the operating frequency of sources 100, 101, and 102, as discussedpreviously. Clearly, the same method can be used for serialinterconnections with more than two points where phase/magnitudecalibration is needed. Also, it is straightforward to apply this methodto cases other than the case discussed above, such as when input signalgenerator 2 is connected to a different node than X. In these othercases, the detection process of the quantities Φ₁, Φ₂, ΔΦ, α₁, α₂, and αis the same but the calculation of compensating states for calibrationcircuits 5 is based on different equations, which result from theparticular propagation conditions of each case.

A Second Method for Calibrating a Serial Interconnection

A limitation of the first calibration method described above is that itis not possible to detect the phase/magnitude changes over serialinterconnect 1 a while input signal generator 2 is driving serialinterconnect 1 a. Moreover, turning on any of signal sources 100, 101,or 102 would interfere with the propagation of the signals from inputsignal generator 2 and the latter signals would produce errors in theoutput of PD/MR detector 4. Clearly, this problem is the consequence ofthe fact that the same serial interconnection is used both for sensingthe phase/magnitude changes and for operating the system with calibratedphases and magnitudes. Therefore, if it is necessary to repeat orrecheck the calibration of serial interconnection 1 a, generator 2 mustbe disconnected from serial interconnection 1 a by turning off switch 3.In some applications, this is not acceptable. For example, if serialinterconnection 1 a carries signals used in a live communicationnetwork, switching off input signal generator 2 interrupts thecommunication. Yet, field operation conditions may change thetransmission properties of serial interconnection 1 a requiring a repeatof the phase/magnitude calibration process. The first method provides nopossibility of calibrating the serial interconnection without stoppingthe operation of the serial interconnection.

A second calibration method described next remedies the aboveshortcoming of the first method. This second method will be describedwith the help of the system illustrated in FIG. 3 but the principle ofthis method is more general than the implementation illustrated in FIG.3. Rather than using a single serial interconnection, the second methoduses two matched serial interconnections: serial interconnection 1 andserial interconnection 1 a. By matched interconnections we mean thatthey are practically identical in propagation properties for a section Xto W on serial interconnection 1 and a corresponding section X′ to W′ onserial interconnection 1 a, respectively. A simple practical realizationof matched serial interconnections is by matched transmission lines on alow cost printed circuit board (PCB) using symmetric layouts placed inclose (parallel) proximity to each other.

The main difference between the system in FIG. 3 and that of FIG. 1 isthe separation between the sensing serial interconnection and theoperating serial interconnection. Serial interconnection 1 a is used forsensing the phase and magnitude variations between points X′, A′, B′ andY′ with the same procedure as were used in the first method employingPD/MR detector 4 and sources 100, 101, and 102. Input signal generator 2drives serial interconnection 1, which carries the signals from thisgenerator to all points in serial interconnection 1, including points X,A, B, and W. No switch is necessary to disconnect input signal generator2 from serial interconnection 1 since the sensing operation is done onserial interconnection 1 a.

The points X′, A′, B′, and W′ in serial interconnection 1 a are selectedto be equivalent to points X, A, B, and W from the signal transmissionpoint of view. This selection is possible because the two serialinterconnections are assumed to be matched. Therefore, the phase andmagnitude differences between any two points in serial interconnection 1a are equal to the phase and magnitude differences between theequivalent two points in serial interconnection 1. It follows that thephase and magnitude changes sensed in serial interconnection 1 a can beused to calibrate serial interconnection 1. The actual calibration isdone with CTR 10 and calibration circuits 5 by using the same procedureas was used according to the first method. Clearly, the system in FIG. 3can calibrate the operating serial interconnection 1 as often asnecessary without interrupting the flow of the signals from input signalgenerator 2. In addition, the frequency of input signal generator 2 isautomatically available at all points X, A, B, and Y, which are closephysically to the equivalent points X′, A′, B′, and Y′, respectively.

A Third Method for Calibrating a Serial Interconnection

In both the first and the second methods described above, the sensing ofphase and magnitude differences between points on a serialinterconnection is done by sending signals in both directions over theserial interconnection from the respective points. As indicated before,it is essential that there are no reflections of signals at any pointsor otherwise sensing errors occur. Reflections create standing wavepatterns that change the equations given in the description of the firstmethod in manners very difficult to predict in practice. The mostcritical points where detrimental reflections can occur in practice arethe end points X, W, X′ and Y′ in the system of FIG. 3. Thesereflections are triggered by imperfect matching networks terminating theserial interconnections. Since these matching networks must absorb theentire power of the signals propagating over the serial interconnection,even small matching errors can still create bothersome reflections.Unlike the end points, the intermediate points A, B, A′ and B′ in FIG. 3are less prone to generating significant reflections because thecouplers can be designed with low coupling coefficients, which naturallyreduce reflections even in the presence of small mismatches. For thefirst and second calibration methods, the problem of end-pointreflections can be mitigated only by using excellent terminations.

A third calibration method described next extends the concepts of thefirst and second calibration methods for the case when some reflectionsare allowed to occur at the end points of the serial interconnection.This method is important in practice because building serialinterconnections with essentially perfect matching at the ends(practically zero reflections) is more difficult and costly thanbuilding serial interconnections with good but not perfect matching atthe ends. This third method will be described with the help of thesystem illustrated in FIG. 4; but the principle of this method is moregeneral than what is shown in FIG. 4.

The system of FIG. 4 uses three matched serial interconnections anddirectional couplers rather than non-directional couplers. A directionalcoupler couples only signals propagating in a particular direction andignores the signals propagating in the opposite direction. A serialinterconnection 1 carries the signals of input signal generator 2 to thepoints A and B (as before, only two points are considered without anyloss of generality). Calibration circuits 5 receive these signalsthrough directional couplers arranged such as to couple any signalpropagating from left-to-right on serial interconnection 1. Theadvantage of using directional couplers is that any reflections from theend point W travelling back from right-to-left are ignored by thecouplers (substantially attenuated) and do not enter calibrationcircuits 5. This is basically equivalent to having a perfect terminationat point W. When the reflections from point W reach the end point X andif the termination at point X is not perfect, the reflections from pointW get reflected back into the left-to-right direction. In theory, thesesecond-order reflections produce phase and magnitude errors in thesystem because they do enter calibration circuits 5. However, inpractice, by the time the signal of input signal generator 2 propagatesover serial interconnection 1 forward, backward, and forward again, theloss over this long path and the power absorptions at the end points (weassume not perfect but reasonably good terminations) usually reduce theremaining detrimental reflections to inconsequential levels.

The sensing of the phase and magnitude changes over serialinterconnection 1 is done just as for the first and second methods butby using two matched serial interconnections (serial interconnection 1 band serial interconnection 1 c) and directional couplers. Serialinterconnection 1 b carries signals only from left-to-right in thesection between points X′ and W′ and serial interconnection 1 c carriessignals only from right-to-left in the section between points X″ and W″.The set of points X, A, B, and W is equivalent to the set of points X′,A′, B′ and W′ and it is also equivalent to the set of points X″, A″, B″and W″ because serial interconnections 1, 1 b, and 1 c are matched overthe sections A to W, A′ to W′, and A″ to W″. In this embodiment,connection points X′, A′, and B′ and connection points X″, A″, and B″,respectively, are electrically connected together to represent nodes sothat connection points X′ and X″ represent a node, connection points A′and A″ represent another node, and connection points B′ and B″ representyet another node. Signal sources 100, 101, and 102 inject equal signalsinto serial interconnections 1 b and 1 c. Since the sections X to W, X′to W′, and X″ to W″ are matched, it follows that the phase and magnitudechanges sensed in serial interconnections 1 b and 1 c can be used tocalibrate serial interconnection 1. Compared to the first and secondcalibration methods, the added benefit is that any reflections in serialinterconnections 1, 1 b, and 1 c, which are not excessive, do notproduce practical errors.

A Fourth Method for Calibrating a Serial Interconnection

In the second and the third methods described above, we sense the phaseand the magnitude differences between points on serial interconnectionsthat are different from serial interconnection 1 that is used fordistributing the signal of input signal generator 2. As a result, thecalibration signals used over serial interconnections 1 a, 1 b, and 1 cmay be different from the signals distributed over serialinterconnection 1. For example, if the signal of input signal generator2 is a bandpass modulated signal (e.g. typical communication signal),the calibration signals on serial interconnections 1 a, 1 b, and 1 ccould be a single non-modulated tone. The frequency of this tone must besuch that the transmission properties (phase and magnitude changes) ofthe serial interconnections at all frequencies used in the system arethe same or can be derived from values valid at one frequency within theset of frequencies considered. Usually, this is the case when thefrequency of the tone is close enough to the frequencies of the bandpassmodulated signal and when the bandwidth of the bandpass modulated signalis within a limit.

In some cases, the signals of input signal generator 2 could be used ascalibrating signals as well. A simple example is LO (local oscillator)distribution when input signal generator 2 produces a CW (continuouswave) signal. In such cases, the third method can be modified as shownin FIG. 5 to obtain a fourth method. More specifically, serialinterconnections 1 and 1 b are replaced by a serial interconnection 1 d,which carries the signal of input signal generator 2 and at the sametime performs the calibration function of serial interconnection 1 b inthe third method (see FIG. 4). Switches 600, 601, 602 and signalinjection circuits 700, 701, 701 are added to provide the capability ofusing the signal from input signal generator 2 for calibration. Switches600, 601, and 602 are controlled by CTR 10. Signal injection circuits700, 701, and 701 receive signals from a corresponding point on serialinterconnection 1 c when switches 600, 601, and 602, respectively, areon and inject them into serial interconnection 1 d. The phases andmagnitudes of the injected signals at points X″, A″, and B″ must berelated to the phases and magnitudes of the signals at points X, A, andB, respectively, in known relationships (e.g. if they are matchedportions of the serial interconnections). For example, the injectedsignals at points X″, A″, and B″ could have the same phases andmagnitudes as the signals on serial interconnection 1 at points X, A,and B. A better choice for minimizing detrimental reflections at pointsX″, A″, and B″ would be to inject signals with reduced magnitudes.

The operation of the fourth calibration method shown in FIG. 5 mimicsthe operation of the other calibration methods described earlier withthe difference that in this case CTR 10, instead of turning on/offsignal sources 100, 101, and 102 (see FIGS. 1, 2, and 4), turns on/offswitches 600, 601, and 602 according to the same scheme of the othermethods. If the signals injected at points X″, A″, and B″ equal thesignals at points X, A, and B, respectively, the equations describingthe relationships between the various transmission parameters (phasesand magnitude ratios) used by the first method are valid as well for thefourth method. However, if the signals injected at points X″, A″, and B″have a different relationship to the signals at points X, A, and B,respectively, the equations describing the relationships between thevarious transmission parameters change accordingly. In any event, theequations can be solved by simple elementary algebra.

Generalizations

Starting with the four methods described above for phase and magnitudecalibration of a serial interconnection, other possibilities may bederived. For example, the first method can be applied with directionalcouplers if a second serial matched interconnection is introduced. Thiswould be equivalent to using serial interconnections 1 c and 1 d of thefourth method of FIG. 5 with signal sources 100, 101, and 102 injectingequal signals into the two serial interconnections instead of usingswitches 600, 601, and 602 and signal injection circuits 700, 701, 701.Just as in the case of the first method, this variation would not becapable of calibrating and distributing the signals of input signalgenerator 2 at the same time.

We have already mentioned that the four methods discussed can be usedwith signals that are more complex than CW signals. For example, thefourth method may be applied with a modulated bandpass signal. In thatcase, however, the PD/MR detector must perform appropriate signalprocessing techniques, which are different from what would be appliedwhen CW signals are use. For example, these signal processing techniquesmight be based on correlation calculations to extract phase andmagnitude differences between two signals. Similarly, other techniquescould also use appropriately modulated calibration signals provided bythe signal sources 100, 101, and 102 in order to reduce the noise in thecalibration process and thus increase the precision of the calibration.

Programmed Controller

Referring to FIG. 6 depicting an exemplary embodiment, the controller(or processor system) is programmed to perform the illustratedoperations to calibrate the serial interconnection system.

First the controller causes a switch to disconnect the signal sourcefrom the system (if required). With the signal source disconnected, thecontroller causes a reference signal to be injected into the first nodeat one end of the serial interconnection system (1000). In someembodiments, this node is the same as the node to which the signalsource was connected. While the reference signal is being injected intothe first node, the controller causes the detector to measure the phasedifference and the magnitude ratio of the injected reference signal anda signal appearing at a second end node of the serial interconnectionsystem (1010). The controller records these measurements in memory foruse at the end of the calibration process.

After making these initial measurements, the controller performs thefollowing operations for each node along the serial interconnectionsystem. With the signal source disconnected, the controller selects anode (1020) and causes a reference signal to be injected only into theselected node (1030). In other words, no references signals are injectedinto any of the nodes except the selected node. While the referencesignal is being injected into the selected node, the controller causesthe detector to measure the phase difference and the magnitude ratio ofthe signal appearing at the first node and a signal appearing at thesecond end node of the serial interconnection system (1040). Thecontroller records these measurements in memory for use at the end ofthe calibration process.

This procedure is repeated for each node in the system untilmeasurements have been made and recorded for all of the nodes (1050).

When the procedure is completed for all nodes, the controller uses themeasured phase differences and magnitude ratios for the first node andthe plurality of serially connected nodes and computes phase andmagnitude corrections for each of the plurality of serially connectednodes (1060). This computation is done as described previously.

After the controller has computed phase and magnitude corrections forall of the serially connected nodes, the controller applies thesecorrections to the serially connected nodes, e.g. by adjusting the phaserotators and gain amplifier appropriately and in accordance with thecomputed corrections (1070).

After the controller completes this set of operations, the serialinterconnection is calibrated. As environmental conditions change orsimply as a result of the passage of time, the interconnection willdrift away from calibration and the procedure will need to be repeated.The controller can trigger the next calibration process eitherperiodically at some preselected delay or upon detecting changes thatmight result in drifts away form calibration (e.g. temperature and/orhumidity changes) (1080).

Application to Phased Array Antenna System Designs

The above-described approaches for distributing coherent,phase-synchronized and equal magnitude signals have particularapplication to designing analog and digital phased array antennasystems. An example of an active analog phased array in which theseconcepts could be applied is illustrated in FIG. 7. This architecture issimilar to architectures described in U.S. Pat. No. 8,611,959, all ofwhich is incorporated herein by reference.

The active antenna array contains a plurality of antenna elements 150placed on a grid, which may be linear, planar, or conformal to asurface. The physical separation of the antenna elements is related tothe frequency of operation of the array and very often equals half theaverage wavelength of the signals transmitted or received. This isnecessary for the array to generate narrow beams with low side lobes.Since typical arrays have a large number of elements, they arefundamentally large electrical systems. In other words, the size of thearray system is large with respect to the Radio Frequency (RF)wavelengths used.

The active antenna array also includes multiple active Tx/Rx modules234. Each Tx/Rx module 234 drives a corresponding one of antennaelements 150 for transmission and receives signals from thatcorresponding antenna element 150 for reception. For that purpose, eachTx/Rx module 234 contains amplifiers, filters, adjustable phase shifters30, adjustable gain stages 40, and mixers 70. A distribution/aggregationnetwork 50 distributes IF signals to the Tx/Rx modules 234 andaggregates received IF signals from the Tx/Rx modules 234. Anotherdistribution network, namely, an LO distribution network 60, distributesan LO signal from a LO signal source 80 to the Tx/Rx modules 234. Mixer7 in each Tx/Rx module 234 uses the distributed LO signal to up-convertthe analog transmit IF signal to RF and it uses the distributed LOsignal to down-convert the received RF signal to IF. Observe that in thedescribed embodiment the phase shifters 30 (also referred to as phaserotators) are located in the LO signal path. This allows for much easierdesigns of these components because shifting the phase of a sinusoidalsignal is much easier than shifting the phase of a modulated signal.

For simplicity of illustration, distribution/aggregation network 50 isshown as a single network; whereas in the described embodiment it is infact two separate networks, one for distributing IF signal to Tx/Rxmodules 234 and one for aggregating received IF signals from the Tx/Rxmodules 234. Similarly, also for simplicity of illustration, thetransmit and receive paths within the Tx/Rx modules 234 are shown as asingle path; whereas, in the described embodiment they are separatepaths, one path for up-converting the IF signal to RF and deliveringthat RF signal to a corresponding antenna element 150 and the other pathfor down-converting the received RF from antenna element 150 to IF anddelivering that received IF signal to the aggregation network portion ofthe distribution/aggregation network 50.

The array system further includes a baseband processor 200 and an IFstage 90 with a transmit side and a received side. During transmission,baseband processor 200 sends a digital signal to the transmit side of IFstage 90, which converts this signal into an analog IF signal usingdigital-to-analog converters and filters and applies that analog IFsignal to the input of the Tx side of distribution/aggregation network50 which, in turn, distributes the IF signal to all Tx/Rx modules 234.During reception, the aggregated received IF signal from the Rx side ofdistribution/aggregation network 50 is delivered to the receive side ofIF stage 90 which converts the received IF signal to digital and passesthat to baseband processor 200.

In the case where the IF signals passing through the stages 90 arebaseband signals (zero IF), the IF stages 90 and the mixers 70 arecomplex blocks, i.e. they process in-phase (I) and quadrature (Q)signals. In the present discussion, we have assumed non-zero IF values(i.e., no I/Q processing) but the discussion is also valid for the zeroIF cases.

There are two control blocks, G CTR 110 and CTR 120, for separately andindependently setting and/or changing the settings of phase shifters 30and gain stages 40 within Tx/Rx modules 234. This is typically done overdigital control buses.

A program running in baseband processor 200 (or some other digitalcontroller that is not shown for simplicity) drives control blocks 110and 120. Each set of phase and gain values for all antenna elementsimplements a specific radiation pattern such as a narrow beam or a morecomplex shape and also implements the calibration corrections that werecomputed as described earlier. By changing these sets of phase andmagnitude values appropriately, the array radiation (both transmit andreceive) is shaped to implement advanced functions such as beam steeringfor tracking a movable target, beam scanning, fanning (changing beamsize), etc.

The above-described calibration techniques can be applied to the Tx/Rxdistribution networks as well as to the LO distribution networks in suchas phased array antenna system.

Application to Phased Array Antenna System Calibration

The above-described approaches for calibrating a serial interconnectionhave also particular application to phased array calibration. An exampleof this application is shown in the diagram of FIG. 8. The phase arraysystem in this diagram consists of a baseband processor 200, an arrayframe 201, and a plurality of Tx/Rx modules 235 coupled to a pluralityof antenna elements 150. The Tx/Rx modules 235 are standard radiofrequency (RF) modules similar to the blocks 234 in FIG. 7. The arrayframe 201 is a block containing all necessary circuits for a particularimplementation of the phased array. For example, in the case of theanalog phased array in FIG. 7, the array frame 201 contains the network50, the network 60, the LO signal source 80, the IF stage 90, and thecontrol blocks 110 and 120. For a digital phased array, the array frame201 contains a plurality of data converters and filters, sampling clockcircuits, digital transport circuits, etc. The application describedhere is valid for any type of phased arrays: analog, digital, or hybrid(partially analog and partially digital).

In general, the practical realization of any phased array requires thatall signal paths from the baseband processor 200 to the antenna elements150 in transmit mode and all signal paths from the antenna elements 150to the baseband processor 200 in receive mode are essentially equal interms of propagation phase shift and magnitude variation. This isdifficult to accomplish without calibration. A serial interconnectionsystem 202 calibrated according to the methods described above can beused for this purpose. This is illustrated in FIG. 8. Couplers 21 couplethe antennas 150 to the serial interconnect system 202. The lattercontains all necessary circuits for calibration as per examples in FIG.1, 3, 4, or 5. The baseband processor 200 controls the serialinterconnection system 202 and communicates with it thoughcontrol/communication means 203.

For the calibration of the phase array transmit subsystem, the basebandprocessor 200 transmits calibration signals through the phased array toall antenna elements sequentially (i.e., one antenna at a time) and itreceives respective signals back from the serial interconnection system202. These signals couple into the interconnection system 202 throughthe couplers 21. Based on all phase and magnitude variation values thebaseband processor 200 obtains through this process and since the serialinterconnection system is calibrated, the baseband processor 200 cancalculate the differences in phase and magnitude between thetransmission paths through the phased array from the baseband processorto the respective antenna elements. Using these calculated values, thebaseband processor 200 adjusts the phase and magnitude of each transmitpath appropriately to equalize them.

For the calibration of the phase array receive subsystem, the basebandprocessor 200 transmits calibration signals through the serialinterconnection system 202 to all antenna elements sequentially (i.e.,one antenna at a time) and it receives respective signals back throughthe phased array. These signals couple into the phased array through thecouplers 21. Based on all phase and magnitude variation values thebaseband processor 200 obtains through this process and since the serialinterconnection system is calibrated, the baseband processor 200 cancalculate the differences in phase and magnitude between the receivepaths through the phased array from the respective antenna elements tothe baseband processor. Using these calculated values, the basebandprocessor 200 adjusts the phase and magnitude of each receive pathappropriately to equalize them.

Other embodiments are within the scope of the following claims.

What is claimed is:
 1. A method for calibrating a serial interconnectionsystem having a first node, a second node, a plurality of calibrationnodes that are electrically connected in series by the serialinterconnection system, and a plurality of connection nodescorresponding to the plurality of serially connected calibration nodes,said plurality of connection nodes electrically connected in series bythe serial interconnection system, said calibration method comprising:for each of the plurality of calibration nodes performing a measurementprocedure involving: injecting a corresponding reference signal intothat calibration node; and while the corresponding reference signal isbeing injected into that calibration node, measuring the phasedifference of signals appearing at the first and second nodes; from themeasured phase differences for the plurality of calibration nodes,computing phase corrections for each of the plurality of calibrationnodes; and applying the phase corrections computed for each of theplurality of calibration nodes to the corresponding plurality ofconnection nodes.
 2. The method of claim 1, further comprising:injecting a first reference signal into the first node; while the firstreference signal is being injected into the first node, measuring thephase difference of that injected first reference signal into the firstnode and a signal appearing at the second node; wherein computing phasecorrections for each of the plurality of calibration nodes also employsthe measured phase difference for the first node and the measured phasedifferences for the plurality of calibration nodes.
 3. The method ofclaim 1, wherein for each of the plurality of calibration nodes themeasurement procedure also involves while the corresponding referencesignal is being injected into that calibration node, measuring themagnitude ratio of the signals appearing at the first and second nodes,and the method further comprises: from the measured magnitude ratios forthe plurality of calibration nodes, computing magnitude corrections foreach of the plurality of calibration nodes; and applying the magnitudecorrections computed for each of the plurality of calibration nodes tothe corresponding plurality of connection nodes.
 4. The method of claim3, further comprising: injecting a first reference signal into the firstnode; while the first reference signal is being injected into the firstnode, measuring the phase difference and the magnitude ratio of thatinjected first reference signal and a signal appearing at the secondnode; wherein computing phase and magnitude corrections for each of theplurality of calibration nodes also employs the measured phasedifference and magnitude ratio for the first node.
 5. The method ofclaim 1, wherein the serial interconnection system comprises a firstserial interconnection serially interconnecting the first node, theplurality of connection nodes, and the second node, and wherein theplurality of calibration nodes is the same as the plurality ofconnection nodes.
 6. The method of claim 1, wherein the serialinterconnection system comprises a first serial interconnection having aportion thereof serially interconnecting the first node, the pluralityof calibration nodes, and the second node and a second serialinterconnection having a portion thereof serially interconnecting theplurality of connection nodes, wherein the first serial interconnectionand the second serial interconnection are separate.
 7. The method ofclaim 6, wherein the portion of the first serial interconnection thatserially interconnects the plurality of calibration nodes and theportion of the second serial interconnection that serially interconnectsthe plurality of connection nodes are electrically matched.
 8. Themethod of claim 1, wherein the serial interconnection system comprises afirst serial interconnection having a portion thereof seriallyinterconnecting the second node and the plurality of calibration nodes,a second serial interconnection having a portion thereof seriallyinterconnecting the first node and the plurality of calibration nodes,and a third serial interconnection having a portion thereof seriallyinterconnecting the plurality of connection nodes.
 9. The method ofclaim 8, wherein the portion of the first serial interconnection thatserially interconnects the plurality of calibration nodes, the portionof the second serial interconnection that serially interconnects theplurality of calibration nodes, and the portion of the third serialinterconnection that serially interconnects the plurality of connectionnodes are electrically matched.
 10. The method of claim 1, wherein whileperforming the measurement procedure for any one of the plurality ofcalibration nodes, applying no other reference signals to any of theother calibration nodes among the plurality of calibration nodes. 11.The method of claim 1, wherein the plurality of connection nodes is thesame as the plurality of calibration nodes.
 12. The method of claim 1,wherein the corresponding reference signals for the plurality ofcalibration nodes have the same frequency.
 13. The method of claim 1,wherein the serial interconnection system also includes an input node,said method further comprising: injecting a first reference signal intothe input node and the first node; while the first reference signal isbeing injected into the input node and the first node, measuring thephase difference of that injected first reference signal at the inputnode and a signal appearing at the second node, wherein computing phasecorrections for each of the plurality of calibration nodes also employsthe measured phase difference for the input node and the measured phasedifferences for the plurality of calibration nodes.
 14. The method ofclaim 13, wherein for each of the plurality of calibration nodes themeasurement procedure also involves while the corresponding referencesignal is being injected into that calibration node, measuring themagnitude ratio of the signals appearing at the first and second nodes,and the method further comprises: from the measured magnitude ratios forthe plurality of calibration nodes, computing magnitude corrections foreach of the plurality of calibration nodes; and applying the magnitudecorrections computed for each of the plurality of calibration nodes tothe corresponding plurality of connection nodes.
 15. The method of claim14, further comprising: while the first reference signal is beinginjected into the input node and the first node, measuring the phasedifference and magnitude ratio of that injected first reference signalat the input node and a signal appearing at the second node, whereincomputing phase and magnitude corrections for each of the plurality ofcalibration nodes also employs the measured phase difference andmagnitude ratio for the input node.
 16. The method of claim 13, whereinthe serial interconnection system comprises a first serialinterconnection having a portion thereof serially interconnecting thefirst node and the plurality of calibration nodes, and a second serialinterconnection having a portion thereof serially interconnecting theinput node and the plurality of connection nodes.
 17. The method ofclaim 16, wherein the portion of the first serial interconnection thatserially interconnects the first node and the plurality of calibrationnodes and the portion of the second serial interconnection that seriallyinterconnects the input node and the plurality of connection nodes areelectrically matched.
 18. An apparatus comprising: a serialinterconnection system having a first node, a second node, a pluralityof calibration nodes that are electrically connected in series by theserial interconnection system, and a plurality of connection nodescorresponding to the plurality of serially connected calibration nodes,said plurality of connection nodes electrically connected in series bythe serial interconnection system; a phase detector electricallyconnected to the first and second nodes of the serial interconnectionsystem for measuring a phase difference of signals sensed at the firstand second nodes; a plurality of switchably controlled signal sources,each switchably controlled signal source connected to a differentcorresponding one of the plurality of calibration nodes; and acontroller system programmed to perform the functions of: for each ofthe plurality of calibration nodes, performing a measurement procedureinvolving: causing the switchably controlled signal source for thatcalibration node to inject a corresponding reference signal into thatcalibration node; and while the corresponding reference signal is beinginjected into that calibration node, causing the phase detector tomeasure the phase difference of signals appearing at the first andsecond nodes; from the measured phase differences for the plurality ofcalibration nodes, computing phase corrections for each of the pluralityof calibration nodes; and applying the phase corrections computed foreach of the plurality of calibration nodes to the correspondingplurality of connection nodes.
 19. The apparatus of claim 18, furthercomprising: a switchably controlled first signal source connected to thefirst node; and wherein the controller system is further programmed toperform the functions of: causing the switchably controlled first signalsource to inject a first reference signal into the first node; while thefirst reference signal is being injected into the first node, causingthe phase detector to measure the phase difference of that injectedfirst reference signal and a signal appearing at the second node. 20.The apparatus of claim 18, further comprising a magnitude detectorelectrically connected to the first and second nodes of the serialinterconnection system for measuring a magnitude ratio of signals sensedat the first and second nodes, and wherein for each of the plurality ofcalibration nodes, the measurement procedure for that node furtherinvolves, while the corresponding reference signal is being injectedinto that calibration node, causing the magnitude ratio detector tomeasure the magnitude ratio of signals appearing at the first and secondnodes; and wherein the controller system is further programmed toperform the functions of: from the measured magnitude ratios for theplurality of calibration nodes, computing magnitude corrections for eachof the plurality of calibration nodes; and applying the magnitudecorrections computed for each of the plurality of calibration nodes tothe corresponding plurality of connection nodes.
 21. The apparatus ofclaim 20, further comprising: a switchably controlled first signalsource connected to the first node; and wherein the controller system isfurther programmed to perform the functions of: causing the switchablycontrolled first signal source to inject a first reference signal intothe first node; while the first reference signal is being injected intothe first node, causing the phase and magnitude ratio detectors tomeasure the phase difference and magnitude ratio of that injected firstreference signal and a signal appearing at the second node.
 22. Theapparatus of claim 18, wherein the serial interconnection systemcomprises a first serial interconnection serially interconnecting thefirst node, the plurality of connection nodes, and the second node, andwherein the plurality of calibration nodes is the same as the pluralityof connection nodes.
 23. The apparatus of claim 18, wherein the serialinterconnection system comprises a first serial interconnection having aportion thereof serially interconnecting the first node, the pluralityof calibration nodes, and the second node and a second serialinterconnection having a portion thereof serially interconnecting theplurality of connection nodes, wherein the first serial interconnectionand the second serial interconnection are separate.
 24. The apparatus ofclaim 23, wherein the portion of the first serial interconnection thatserially interconnects the plurality of calibration nodes and theportion of the second serial interconnection that serially interconnectsthe plurality of connection nodes are electrically matched.
 25. Theapparatus of claim 18, wherein the serial interconnection systemcomprises a first serial interconnection having a portion thereofserially interconnecting the second node and the plurality ofcalibration nodes, a second serial interconnection having a portionthereof serially interconnecting the second node and the plurality ofcalibration nodes, and a third serial interconnection having a portionthereof serially interconnecting the plurality of connection nodes. 26.The apparatus of claim 25, wherein the portion of the first serialinterconnection that serially interconnects the plurality of calibrationnodes, the portion of the second serial interconnection that seriallyinterconnects the plurality of calibration nodes, and the portion of thethird serial interconnection that serially interconnects the pluralityof connection nodes are electrically matched.
 27. The apparatus of claim18, wherein the controller system is further programmed to cause theswitchably controlled signal sources for the plurality of calibrationnodes to inject corresponding reference signals into the plurality ofcalibration nodes only one at a time.
 28. The apparatus of claim 18,wherein the corresponding reference signals for the plurality ofcalibration nodes have the same frequency.
 29. An apparatus comprising:a serial interconnection system having a first node, a second node, aplurality of calibration nodes that are electrically connected in seriesby the serial interconnection system, and a plurality of connectionnodes corresponding to the plurality of serially connected calibrationnodes, said plurality of connection nodes also electrically connected inseries by the serial interconnection system; a phase detectorelectrically connected to the first and second nodes of the serialinterconnection system for measuring a phase difference of signalssensed at the first and second nodes; a plurality of switches forswitchably electrically connecting each connection node among theplurality of connection nodes to a corresponding different calibrationnode among the plurality of calibration nodes; a controller systemprogrammed to perform the functions of: for each of the plurality ofcalibration nodes, performing a measurement procedure involving: causingthe switch for that calibration node to inject a corresponding referencesignal from the corresponding connection node into that calibrationnode; and while the corresponding reference signal is being injectedinto that calibration node, causing the phase detector to measure thephase difference of signals appearing at the first and second nodes;from the measured phase differences for the plurality of calibrationnodes, computing phase corrections for each of the plurality ofcalibration nodes; and applying the phase corrections computed for eachof the plurality of calibration nodes to the corresponding plurality ofconnection nodes.
 30. The apparatus of claim 29, further comprising amagnitude detector electrically connected to the first and second nodesof the serial interconnection system for measuring a magnitude ratio ofsignals sensed at the first and second nodes, and wherein for each ofthe plurality of calibration nodes, the measurement procedure for thatnode further involves, while the corresponding reference signal is beinginjected into that calibration node, causing the magnitude detector tomeasure the magnitude ratio of signals appearing at the first and secondnodes; and wherein the controller system is further programmed toperform the functions of: from the measured magnitude ratios for theplurality of calibration nodes, computing magnitude corrections for eachof the plurality of calibration nodes; and applying the magnitudecorrections computed for each of the plurality of calibration nodes tothe corresponding plurality of connection nodes.
 31. The apparatus ofclaim 30, wherein the serial interconnection system also includes aninput node, said apparatus further comprising a signal sourceelectrically connected to the input node.
 32. The apparatus of claim 31,further comprising a first switch for switchably electrically connectingthe input node to the first node, and wherein the controller system isfurther programmed to perform the functions of: causing the first switchto inject a signal into the first node from the input node; while thesignal is being injected into the first node from the input node,causing the phase and magnitude detectors to measure the phasedifference and the magnitude ratio of that signal injected into thefirst node from the input node and a signal appearing at the secondnode, wherein computing phase and magnitude corrections for each of theplurality of calibration nodes also employs the measured phasedifference and magnitude ratio for the input node.